1. Field of the Disclosure
The following is directed to drill bits for drilling subterranean formations and particularly drill bits comprising backup cutting elements having different cutting characteristics.
2. Description of the Related Art
The recovery of hydrocarbons or minerals from the earth is typically accomplished using a drill string that is driven from the surface of the earth into depths of the upper crust through a borehole. Various removal mechanisms can be used to advance the depth of the borehole including abrasion, fracturing, and shearing the subterranean formations at the bottom of the borehole. In fact, depending upon the type of subterranean formation, different types of drill bits are typically used, since different types of removal mechanisms are suitable for different types of formations.
Particular types of drill bits include fixed-cutter drill bits and roller cone drill bits. Roller cone drill bits can employ rolling elements, oftentimes cone shaped structures, capable of rotation relative to the drill bit head that can incorporate abrasive teeth extending from the surface. Roller cone drill bits typically advance through contacted subterranean formations through fracturing and abrading mechanisms. Fixed-cutter drill bits, by contrast, employ cutting elements made of hard material that are situated on the drill bit in a manner to shear and cut through contacted rock formations. Certain factors that determine the type of drill bit to be used include the hardness of the formation and the range of hardnesses to be encountered. Generally, conventional industry knowledge dictates that roller cone drill bits, particularly those incorporating tungsten carbide insert (TCI) cutting structures, have the best rate of penetration and lifetime in hard and superhard formations as compared to most fixed-cutter drill bits. While in formations of soft and medium hardness, fixed-cutter bits are commonly used. There remains a need in the art for development of drill bits capable of penetrating various types of rock formations.